1. Field of the Invention
The present invention relates to a heating panel and method of use as a platen or other heating surface, which includes at least one internal fluid-filled channel and an internal heating source.
2. Description of Related Art
Platen presses are routinely used in the manufacture of plywood, chipboard, fiberboard and paneling. The layers or fibers of these products are hot pressed together with a binder to produce the finished panels. A platen press generally includes an upper frame and a lower frame on which heating platens are mounted. As is described in U.S. Pat. No. 5,421,951, a platen press is usually elongate with a rectangular shape and a large, flat heating surface. A standard platen is heated by means of internal narrow passages, which are drilled or otherwise formed in the internal portion of the platen and are positioned adjacent to the heating surface. These passages generally have a one-inch diameter. A heat exchange liquid in the form of oil or water, or heat exchange vapor in the form of steam, is passed through the internal network of narrow passages to provide heat, which is conducted to the heating surface of the platen.
Typically, in prior art platens, the heat exchange liquid or vapor is heated with a heating source at a location external to the platen. Following the heating at the external source, the heat exchange liquid or vapor is directed through a tube to a manifold, which directs it into the network of narrow passages at one end of the platen. During the passage of the heat exchange liquid or vapor through the network of narrow passages in the internal portion of the platen, heat is conducted to the surface of the platen. The heat exchange liquid or vapor then exits through the opposite end of the platen. Following the exit at the opposite end of the platen, the heat exchange liquid is returned to the external heating source for reheating prior to recirculation through the platen.
An inherent functional defect exists in the prior art platens, which involves the heat exchange liquid or vapor losing its temperature during passage through the platen. The loss of temperature in the heat exchange liquid or vapor flowing through the platen creates a temperature gradient that directly affects the temperature of the heat surface of the platen. The temperature gradient causes a gradual temperature drop on the surface of the platen. The temperature of the heating surface is the highest at the end where heat exchange liquid is introduced into the platen and then gradually decreases along the heating surface to the lowest temperature at the end where the heat exchange liquid exits the platen.
The prior art teaches that attempts have been made to mitigate the temperature loss by increasing the pressure and/or flow rate of the heat exchange liquid passing through the network of narrow passages in the platen. However, the improvements made in the art to address the temperature loss have not satisfactorily solved the heat loss problem. Additionally, the improvements have not solved the occurrence of undesirable, localized hot spots on the heating surface of a platen. Accordingly, there is a present need for a platen with at least one internal heating element for equilibrating the temperature of a heat exchange fluid flowing through internal channels of the platen that establishes a consistent temperature on the heat surface for pressing and/or drying operations.